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The electrochemical oxidation of aliphatic carboxylic acids, hexanoic, heptanoic, and lauric acid, under biphasic conditions is studied as a model system for ultrasound enhanced Kolbe electrosynthesis processes. Power ultrasound is used to generate an in situ emulsified medium and to remove reaction products continuously from the electrode surface. A clean and highly efficient process at platinum electrodes with formation of 'one electron' products only occurs in marked contrast to processes in monophasic media. For hexanoic acid the Kolbe dimer product R-R is formed in up to 75% yield with 45% current efficiency at 0.18 A cm-2 current density and in the presence of 190 W cm-2 ultrasound. The mechanism is explained in terms of a dynamically modified electrode surface, at which hydrophobic products are immediately 'trapped' via partitioning into a non-polar organic phase and transported away into the emulsion system. Kolbe electrosynthesis is undertaken both at platinum electrodes and at free-standing polycrystalline boron-doped diamond electrodes, in order to minimize the surface erosion effect induced by power ultrasound. The type and yield of products obtained from the biphasic Kolbe electrolysis process at diamond electrodes are essentially identical to those observed at platinum and based on this observation, the presence of a biphasic reaction layer at the electrode surface is postulated to govern the process. © 2001 Elsevier Science B.V.

Solutions containing hen egg white lysozyme (HEWL) and nitrite were exposed to ultrasonic irradiation in order to study the possible sonochemical modifications. This is the first demonstration of the nitration of tyrosine residues in a protein (lysozyme) by the use of an ultrasonic field alone. Sonochemically nitrated lysozyme was detected using the immunochemical techniques dot blot immunodetection and enzyme-linked immunosorbent assay (ELISA). The sonically oxidised and nitrated protein solutions were analysed by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Hydroxylated species were found in the absence of nitrite, whereas nitration was the major modification in the presence of nitrating agent, implying a competing mechanism between hydroxyl radicals and nitrite. Circular dichroism (CD) indicated that the ultrasonic experimental conditions chosen in this study had little effect on the tertiary and secondary structures of HEWL. Whilst enzymatic assay showed that the presence of nitrite provided a protective effect on the inactivation of the protein under ultrasonic irradiation, nevertheless partially purified, sonically nitrated lysozyme showed a dramatic decrease in lytic activity.

In this paper we report the successful use of a non-metallic electrode material, boron-doped diamond (BDD), for the anodic electro-oxidative modification of hen egg white lysozyme (HEWL). Platinum electrodes can give rise to loss of activity of HEWL in electrosynthetic studies, whereas activity is retained on boron-doped diamond which is proposed as an effective substitute material for this purpose. We also compare literature methods of electrode pre-treatment to determine the most effective in electrosynthesis. Our findings show a decrease in total nitroprotein yield with decreasing nitrite concentration and an increase with increasing solution pH, confirming that, at a BDD electrode, the controlling factor remains the concentration of tyrosine phenolate anion. Purification of mono- and bis-nitrated HEWL and assay of enzymic activity showed better retention of activity at BDD electrode surfaces when compared to platinum. The products from electro-oxidation of HEWL at BDD were confirmed by electrospray ionization Fourier transform ion cyclotron resonance (ESI-FT-ICR) mass spectrometry, which revealed unique mass increases of +45 and +90Da for the mono- and bis-nitrated lysozyme, respectively, corresponding to nitration at tyrosine residues. The nitration sites were confirmed as Tyr23 and Tyr20.

A thin film comprising highly sterically hindered iron phthalocyanine derivatives incorporated into sol–gel networks shows effective sensitivity to carbon monoxide gas, when monitored by UV–visible absorption spectroscopy at 670 nm. The absorbance of a sol–gel thin film incorporating octaphenyl-di-tert-butylphthalocyanine iron(II) was particularly sensitive to carbon monoxide gas and showed a change in absorption after exposure to 1000 ppm CO gas for 1 min, while repetitive exposures produced only a limited loss of response. The optical response of the thin film gradually decreases with increasing temperature, and the binding energy for this sensing phenomenon was calculated to be 0.401 eV. The spectrum recovers at room temperature some 5 min after exposure to the gas.

Tetracyclones are transformed to a mixture of diacylstilbenes and α-pyrones, when they are heated in diphenylether saturated with oxygen.

In producing a method for selective protein nitration, we previously demonstrated the electrochemical nitration of hen egg white lysozyme to be at Tyr23 initially, followed by bisnitration at Tyr20, but with no trisnitration at Tyr53. The nitration site was determined by sequencing a tryptic peptide that included Tyr23 and Tyr20, but possible effects on other regions of the protein were not determined. Moreover, the electrooxidation conditions were harsh, involving an oxidation potential of +1.2 V (vs. saturated calomel electrode [SCE]), no added nitrogen source except the lysozyme itself, and long reaction periods with copper flag electrodes. Here we report a gentler procedure using much shorter reaction times with nitrite as the nitration source, a lower potential (+0.85 V vs. SCE), and a platinum basket electrode. Intact protein analysis by electrospray Fourier transform ion cyclotron resonance mass spectrometry identified mono- and bisnitration products with mass increases of +45 and +90 Da, respectively, consistent with the substitution of NO2 for H. In addition, the results revealed that no other covalent change in the protein occurred following electrooxidation. Nozzle skimmer dissociation of the intact mononitrated species localized the modification site to Tyr20 or Tyr23. Matrix-assisted laser desorption/ ionization time-of-flight and electrospray ionization time-of-flight analysis of the tryptic peptides of mononitrated lysozyme identified the site of nitration as Tyr23. (c) 2006 Elsevier Inc. All rights reserved.

The electrooxidative behaviour of tetraphenylcyclopentadienone (tetracyclone) and a number of its substituted derivatives have been studied by cyclic voltammetry. Preparative electrooxidation reactions have been found for the tetracyclones to yield the corresponding α-pyrones as major product from an oxygen insertion reaction; while in contrast, under similar conditions the sulfoxy analogue, tetraphenylthiophene-S-oxide, is oxidized to (Z)-diphenacylstilbene with loss of the sulfur-function from the heteroaromatic ring.

The electrochemical reduction of silver thiosulphate was studied potentiostatically on platinum electrodes in the absence and presence of ultrasound (20 kHz). This system is irreversible and the reaction is both diffusion and kinetically controlled. The slowest step is the kinetic reaction especially the chemisorption of ions at the electrode surface. Ultrasound greatly improves the mass transport, which can be explained by changing from diffusion to mainly convection. This paper reports the effect of ultrasound upon electrode kinetic and mass-transport parameters at various RDE rotation speeds and ultrasonic intensities. It was found that the heterogeneous rate constant (kf) is improved in the presence of ultrasound due to the increase in the formal or standard heterogeneous rate constant (k0) (approximately by 10-fold under sonication).

In alkaline solution a strongly passivating layer is formed close to a copper metal surface during a positive sweep to potentials beyond approximately +0.5 V (vs. SCE). Simultaneous ultrasonic irradiation during the voltammetric scan promotes the anodic dissolution of copper and greatly increases anodic currents in the less-positive potential region 0–0.5 V (vs. SHE), which corresponds to the formation of a thicker, more porous oxide/hydroxide layer, but does not prevent this passivation process from occurring at potentials above 0.5 V in sodium hydroxide solution up to 3 mol dm −3 concentration. The passivating layer requires maintenance of oxidising conditions, and so the removal of the protective oxide/hydroxide coating, which is effectively performed by ultrasound, facilitates reductive loss of the passivating layer sufficiently readily that an anodic current can be seen during the reduction scan between +0.5 and 0 V while scanning from the positive limit in a negative direction. In 1 M NaOH a curve-crossing phenomenon occurs in silent voltammetry in which scan reversal before the onset of passivation produces a higher anodic current in the reverse (reductive) direction than during the forward positive scan before reversal. Also at this alkali concentration, when the positive range is scanned into the passivation region the maximum anodic peak current in silent voltammetry is independent of scan rate over the range from 5 to 80 mV s −1 . Presonication of the copper surface prior to silent voltammetry greatly increases the peak currents and enhances peak definition in the copper voltammogram, suggesting general activation of the metal surface by ultrasound. The oxidation processes continue to occur at similar potentials, but there is a new peak in the reduction scan, with some shift of reduction potentials.

Thiophene-S-oxides (thiophene monoxides) are relatively new compounds, less stable than the better-known thiophene-S-dioxides. They are useful as synthons for a range of applications, including in the production of pharmaceuticals. They have interesting photochemical properties, but in this presentation we contrast the electro-oxidative voltammetry of differently substituted derivatives. We also compare carbocyclic compounds such as tetracyclone, the electro-oxidation of which at relatively high potentials has never been reported in silent or insonated conditions.

This paper describes recent studies in organic sonoelectrochemistry at Coventry University, including the oxidation of thiophene monoxides, degradation of dye pollutants, formation of conducting polymers and electrosynthetic modification of proteins.

The diffusion through an agarose hydrogel of the ionophoric antibiotic valinomycin dissolved in a mixture of water and ethanol is characterized by electrochemically monitoring the conductivity of a lipid bilayer membrane buried within the gel. Classical Fickian diffusion is observed, with no evidence for traps, and with a best-fit diffusion constant through the gel of 26 μm 2 s −1 for ethanol and 2.0 μm 2 s −1 for valinomycin. The valinomycin appears to be present in solution as large aggregates. The time response is consistent with boundary conditions in which the valinomycin enters the membrane but does not re-emerge on the other side.

The electrochemistry of microdroplets, shown to be nearly monodisperse, of N,N,N‘,N‘-tetraalkyl-para-phenylenediamine oils (TRPD, R = n-butyl, n-hexyl, n-heptyl, and n-nonyl) immobilized on a basal plane pyrolytic graphite electrode and immersed into aqueous electrolyte solution is studied using cyclic voltammetry. Upon oxidation of the TRPD droplet to the cation radical TRPD+•, anion uptake from, or cation loss into the aqueous solution takes place, so as to maintain electroneutrality within the oily deposit. The former process is shown to produce an ionic liquid, with the anion insertion taking place at the triple phase boundary of electrode |TRPD oil| aqueous electrolyte; the latter process, in contrast, takes place at the interface between the two immiscible liquids, and with two-thirds-order kinetics. The possibility of a chemical reaction taking place between the electrogenerated and inserted ions at the three-phase junction, viz. redox-catalysis or otherwise, is illustrated via reference to two sys...

The work at Coventry University on sensing for nitrogen dioxide by monitoring optical changes in an active molecule is reviewed. Initially, changes in polarisability were converted into intensity changes in a λ/4 Langmuir-Blodgett film. More recently, direct measurement of changes of absorbance has been shown to be superior. Ideal gas adsorption is described by the Langmuir isotherm, and the binding energy of the gas to the molecular site is a critical factor. One of the azosubstituted polysiloxanes shows a value of 0.6eV, near optimal for room-temperature operation. To operate at higher temperatures, in order to avoid cross-sensitivity to water, a more active derivative responds in seconds, recovers reproducibly, and can be deposited in sol-gel or network polysiloxane rubber matrices.

A new SECM approach for studying the lateral diffusion of redox-active amphiphiles in Langmuir monolayers at an air/water (A/W) interface is described. To apply this technique practically, a triple potential step transient measurement is utilized at a submarine ultramicroelectrode (UME) placed in the water phase close (1−2 μm) to the monolayer. In the first potential step, an electroactive species is generated at the UME by diffusion-controlled electrolysis of a precursor. This species diffuses to, and reacts with, the redox-active amphiphile at the A/W interface resulting in the formation of the initial solution precursor, which undergoes diffusional feedback to the UME. In this first step, the rate constant for electron transfer between the solution mediator and the surface-confined species can be measured from the UME current−time transient. In the second period, the potential step is reversed to convert the electrogenerated species to its initial form. Lateral diffusion of electroactive amphiphile int...

Earlier findings on electronitration of hen egg-white lysozyme demonstrated a product which was mononitrated at Tyr23, by ion-exchange chromatography, absorbance at 430 nm, dithionite reduction, and Edman sequencing of a nitrated proteolytic peptide. However, the whole protein was not sequenced; therefore, although the enzyme remained active upon nitration, reaction at other residues could not be completely eliminated. This study has now been extended to the redox protein myoglobin. We demonstrate the novel electronitration (electrooxidation in the presence of nitrite) of a specific tyrosine residue in horse heart myoglobin and also in apomyoglobin. Production of the yellow chromophore, 3-nitrotyrosine (3-NT), was apparent in apomyoglobin from A430 but was masked in holomyoglobin by the Soret band. In both cases, the presence of 3-NT in the electronitrated samples was further indicated by the binding of antibody to 3-NT in Western blots. High-resolution electrospray ionization (ESI) Fourier transform ion cyclotron resonance (FTICR) mass spectrometry revealed a reaction product at [M + 45] (consistent with substitution of NO2 for H), indicating that the nitration reaction is the only reaction occurring which gives rise to a change in mass in the electrooxidation. Fragmentation mass spectrometry identified the nitration site as Tyr103, with no nitration at Tyr146. The procedure may be useful in preparing model nitrated proteins for the study of disease mechanisms.

Solutions of both basic and acidic dyes were subject to sonolysis, electrolysis, and sonoelectrolysis. Only basic dyes were decolorized by ultrasound alone. Removal of the acidic dye Sandolan Yellow required the use of an electrooxidation process. The rate of electrochemical decolorization in the absence of ultrasound was dependent on the type of electrolyte, the electrolyte concentration, the reaction temperature, and the current density. The sonoelectrooxidation of Sandalon Yellow needed to be performed in a sealed cell to minimize the effects of ultrasonic degassing.

Insonation of cyclohexanoate electrooxidation at platinum in methanol produces a similar switch in product distribution from one-electron per-molecule dimers towards products from the two-electron route via the carbocation, irrespective of whether the ultrasonic bath employs 38 or 850 kHz frequencies. However, 850 kHz produces a cleaner reaction and higher yields, with more than two-fold greater yield of total extracted products over the silent system, and one-and-a-half times yield enhancement over insonation at 38 kHz. Keywords: Sonoelectrochemistry, Carboxylate electrooxidation, Ultrasound, Frequency dependence

4-Alkoxy-4′-(phenylazophenethyl) alcohol derivatives respond rapidly and reversibly at room temperature when exposed as thin films to nitrogen dioxide and interrogated by change of absorbance at 475 nm. The temperature dependence of sensitivity is described by an Arrhenius activation energy. Values of activation energy obtained from a polymeric derivative deposited as a Langmuir–Blodgett (LB) film and from a low molar-mass derivative trapped in a sol–gel matrix are all close to 0.6 eV, indicating that aggregation effects are negligible, and that this figure represents a sterically-unhindered interaction between nitrogen dioxide and the azo chromophore.

INTRODUCTION The majority of electrochemical studies of biomolecules have been analytical in nature, usually involving electron transfer by redox proteins. Synthetic applications of electrochemistry to proteins, leading to the production of recoverable products, has been far less widely studied. However, the use of proteins in electrosynthesis, exemplified by hen egg-white lysozyme, demonstrates that the reaction parameters of pH, potential difference, electrode material etc., can be varied in order to target different individual amino acid residues including tyrosine, tryptophan and methionine. This methodology provides a novel route to quantities of selectively-modified proteins.

A novel thin film based on an azobenzene chromophore incorporated into a sol–gel network is demonstrated to be sensitive to NO2 gas and shows comparable sensing performance to a Langmuir–Blodgett (LB) film of the same chromophore attached to a polysiloxane backbone. Sensing was carried out by UV–Visible absorption spectroscopy monitoring increase in the n–π* transition at 475 nm with simultaneous decrease in the π–π* transitions at 240 nm and 360 nm on exposure to 100 ppm NO2 gas. Preliminary stability studies show only a limited loss of response (

We report improved techniques for the fabrication of biomimetic membranes protectively sandwiched between two slabs of agarose gel and the evaluation of their characteristics relevant for use in a biosensor based on gated channel proteins. The gel protects the membrane from mechanical contact, from low-energy solvents and from drying out. The new methods allow the preparation in high yield of sensor cells with a front gel thickness less than 100 μm. During fabrication, gel-protected membranes of DOPC (dioleoyl phosphatidylcholine) readily incorporate valinomycin in functional form. DOPC membranes respond as expected and within a few minutes to aqueous solutions of gramicidin applied to the front gel layer. In long-term studies of protected membranes of the synthetic lipid PSPC, no failures were observed over runs of up to 3 weeks and the membrane leakage decreased, reaching within 7 days values comparable to those reported for unsupported bilayer lipid membranes. Initial attempts to incorporate functional nicotinic acetylcholine receptors have shown promise.

This paper describes the effect of ultrasound on electrochemical parameters important in the removal of silver from photographic processing solutions. Decomposition voltages (obtained galvanostatically) and discharge potentials (obtained potentiostatically) for the reduction of the silver complex, Ag(S2O3) 2 3- was studied in dilute aqueous Na2S2O3/NaHSO3 solution on stainless steel and carbon disc electrodes in both the absence and presence of ultrasound. Under silent conditions, silver deposition is the main reaction occurring at the electrode. Under sonication at 20 kHz and 500 kHz, the reduction wave shifts anodically with increasing ultrasonic intensity. Similarly, the discharge of hydrogen and oxygen shifts anodically and cathodically respectively with increasing ultrasonic power. The decrease in decomposition voltage in the presence of ultrasound is due to the combined effect of a decrease in anodic overpotential and an increase in cathodic overpotential.

Siloxane copolymers having as side-chains azobenzene derivatives bearing different electron-withdrawing and donating substituents were deposited as thin films by dip coating, and their behaviour upon exposure to 100 pm NO2 was studied by UV/visible spectroscopy. Electron-donating substituents at the ortho positions on the aromatic rings in the azo unit have significant influence on the absorbance changes produced by exposure to NO2, and this is explained by modelling, which suggests that interaction between the electrophilic nitrogen atom in NO2 and the electron clouds of the azobenzene skeleton is responsible for the sensing process, rather than the formation of a Wheland intermediate or other product of chemical reaction. Especially effective substituents are methoxy groups in either aromatic ring ortho or the azo linkage, which also produce a significant increase in intensity of the long-wavelength n–π* transition. This moves the optical interrogation signal to a wavelength range of particular benefit for potential applications. Copyright © 1998 John Wiley & Sons, Ltd.

Thin films of a selection of stilbene and biphenyl side-chain substituted liquid crystal polymers based on polysiloxanes were deposited using an automated dip-coating technique and exposed to either 100 ppm NO2 gas and/or concentrated nitric acid vapour, the consequent effect being monitored by changes in the UV–visible spectra of the material. No effective response to NO2 was observed from the biphenylene analogue, but the stilbene derivatives showed spectral changes to suggest that an interaction occurs between the vapour and the bridge position of the stilbene side-chain. The stilbenes also show a marked pre-conditioning phenomenon upon exposure to nitric acid vapour prior to exposure to nitrogen dioxide. This procedure gives a material that has a more reversible response on exposure to NO2 gas than an anagolous film that has not been pre-treated. Copyright © 1998 John Wiley & Sons, Ltd.

A new approach is described for the quantitative study of the effect of a monolayer on solute transfer rates across an air/water interface. The technique is illustrated through measurements of oxygen transfer across a monolayer of 1-octadecanol as a function of compression. The experimental approach uses an inverted ultramicroelectrode (UME), positioned in the water phase in a Langmuir trough close to the air/water interface to induce the transfer of oxygen from air to water via the reduction (and depletion) of oxygen. The steady-state current response, measured as a function of UME−interface separation at various monolayer compressions, demonstrates that the rate of oxygen transfer is governed primarily by the accessible free area of the interface.

Langmuir–Blodgett and vacuum-deposited films of two ferrocene derivatives were employed for sensing NO 2 by the interference-enhanced reflectometry technique. A dialkylated derivative, 1,1′-dioctadecyl ferrocene, was two orders of magnitude more sensitive than the diacylated analogue, but gave a less reversible response. The diacyl derivative 1,1′-dioctadecanoyl ferrocene, was less sensitive, but gave a more reversible response; and when employed in a practical device based on an LED-photodiode configuration was able to detect NO 2 at the 1 ppm level. Neither material responded to CO in the conditions employed. Data from atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) suggested that higher concentrations (1%) of NO 2 caused permanent change.

Nucleophilic attack by hydroxyl ions is found to occur preferentially at the C 2 position of the benzothiazolium heterocyclic moiety of the laser dye IR140, and not at the eneamine functionality that consists of the mesocarbon atom and the adjacent diphenylamine moiety, which is the other electrophilic site on the dye. The temperature-dependence of the absorption spectrum of the merocyanine breakdown product suggests that similar ground state isomerism is present in the breakdown product, as is found in the initial dye IR140. It is concluded that the non-fluorescent majority conformer of the merocyanine breakdown product is the one in which the meso-amine substituent is twisted so as to withdraw electron density by induction, and that the fluorescent minority conformer is that in which themeso-amine substituent is conjugated to act as an electron donor by resonance.

Use of electrosynthetic methodology allows the production of hen egg-white lysozyme (HEWL) either mononitrated at tyrosine 23 or bisnitrated at tyrosines 20 and 23, but never nitrated at tyrosine 53. This is a different sequence from that obtained by the chemical nitrating agent tetranitromethane, and when reduced by dithionite, the selectively modified enzyme can be anchored at pH 5 via the unique aromatic amino group to magnetic beads or other suitable matrices. HEWL so immobilised loses less than 10% of cell-wall lytic activity compared with the approximately 50% loss of activity when immobilised by conventional methodology at pH 9 via essentially random reaction at lysine residues and other functionalities which are nucleophilic at this pH. This result offers promise as a general method for selective protein immobilisation in biosensors and similar applications. © 1998 John Wiley & Sons, Ltd.

p-Cresol, as a small-molecule model for tyrosine residues in proteins, undergoes electrooxidative nitration in the presence of a nitrogen source, for example ammonia, in mildly alkaline aqueous solution at potentials in the range 0.8 to 1.4 V (vs sce). Anodized copper is the best electrode material of those studied and nitrogen sources in the increasing order of effectiveness are amides < amines ≅ proteins < ammonia, the latter giving a total of nitrocresols of ~ 30% from an initial p-cresol concentration of 0.5 mM. Azulene also nitrates in these conditions, but phenylethers (4-methyl methoxybenzene and 1,2-dimethoxy benzene) do not. The protein hen egg-white lysozyme (HEWL), in the absence of any other nitrogenous species, acts as a source of nitrating agent in the electrooxidative nitration of p-cresol thus substantiating our earlier finding of selective tyrosine nitration in proteins in the absence of any other nitrogen source. This electronitration reaction, unique in that there is no NO bond in any initial species, provides a novel and environmentally friendly route in mild conditions and is of particular benefit in the selective covalent modification of proteins.

Electrosynthesis provides a novel methodology to produce specific and selective chemical reaction in proteins. Thus electrooxidation of hen egg-white lysozyme (HEWL) at + 1.2 V (vs sce) at a carbon anode in mildly acid buffer produces selective oxidation at methionine-105; while by increase in anodic potential, or by addition of acetonitrile co-solvent, subsequent oxidation at methionine-12 is observed. Further increase of potential in otherwise similar conditions additionally produces a novel cleavage between tryptophan-62 and tryptophan-63, the latter remaining intact and becoming the new N-terminus of the fragment. No reaction occurs at other tryptophan residues in HEWL, and histone H4, which contains no tryptophan residues, does not cleave in these conditions. The previously reported selective nitration at tyrosine residues by use of copper electrodes in alkaline medium is not observed in the acid electrolysis system and shows the fine control over protein modification available by manipulation of electrosynthetic parameters. The methodology offers wide implications.

Polymeric and low molecular mass azobenzenes, ferrocene derivatives and a diphthalocyanine have been deposited on silicon, principally using the Langmuir-Blodgett technique. Interference-enhanced reflectometry was used for gas sensing, with films selected to give low reflectance of green light in air. For a polysiloxane azobenzene material, reflectance changes were up to 75% on exposure to 100 ppm NO 2 in air, with response and recovery times of the order of 10 s, and recovery was effectively complete. The response or deposition characteristics resulted in reduced performance for the other materials; the effect of differing deposition methods is discussed.

The preferential incorporation of perchlorate into the polymer, from electrolyte solutions also containing hexafluorphosphate, a phenomenon previously observed during the preparation of polypyrrole, has now been shown to take place in substituted derivatives of polypyrrole, polythiophene and also in polyazulene. In these ring systems the presence of electrondonating side groups enhances the effect. Preferment of perchlorate to various degrees is seen in all systems so far studied, including a number of different solvents, and is strongest in solvents of low nucleophilicity, such as nitromethane. Polypyrrole and polythiophene from acetonitrile solutions that contain only the respective anions show a higher dopant ratio in perchlorate-containing films compared with hexafluorophosphate films, suggesting that the competitive doping effect between these anions results from preferential perchlorate compensation of cationic species produced during the polymerisation.

The limiting current from Fe(CN) 6 3− Fe(CN) 6 4− redox in dilute aqueous KCl at a platinum electrode appears to be little affected by the frequency of simultaneous ultrasonic irradiation in the range 20–800 kHz, and is not influenced by choice of bath or probe as sonic source, provided measurements are made at constant ultrasonic intensity. The limiting current is dependent on ultrasonic intensity at constant frequency. In contrast, the peak potential of the redox couple varies with ultrasonic frequency in the same range, but does not vary with ultrasonic intensity at constant frequency. Application of ultrasound to a rotating disc electrode provides an increase in limiting current across the frequency range, the magnitude of which varies with both concentration and rotation speed. The average maximum increase is some 1.5-fold which corresponds to an effective rotation rate of 100 000 rpm (1667Hz) for a silent solution in order to achieve the same transport rates. It is shown that changes in macroscopic temperature throughout the experiment are insufficient to cause the observed enhanced diffusion.

A polysiloxane with sidechain azobenzene chromophores has been deposited as Langmuir-Blodgett films on silicon. Using interference-enhanced reflectometry with films selected to give low reflectance of 520 nm light in air, reflectance changes of 75% were recorded on exposure to 100 ppm NO2 in air. Response and recovery times were of the order of 10 s, and recovery was effectively complete. The mechanism of response and factors such as long-term stability have yet to be fully investigated.

Preparative electrooxidation of lysozyme at copper electrodes held at potentials around 1.2 V vs. a saturated calomel reference electrode induces the formation of a yellow chromophore with a concomitant decrease in the pI of the protein. Ion-exchange high-performance liquid chromatography revealed two new lysozyme species with pI values of 10·8 and 10·7 (lysozyme-11.0) which bear the chromophore. Sequence analysis of these two species showed that protein with lower pI was modified at both Tyr 23 and Tyr 20 and the other exclusively at Tyr 23. Ribonuclease A, subtilisin BPN', and BSA were also found to produce the same chromophore using similar electrochemical reaction schemes. Characterization of the chromophore by a variety of techniques revealed that it is apparently 3-nitrotyrosine.

Polysiloxanes were functionalized for Langmuir-Blodgett (LB) deposition of films for optical and bioelectronic applications. Azo dye chromophores give second-harmonic generation and phosphatidylcholine (PC) side-groups yield bilayers suitable for inclusion of active proteins. The polymeric forms are better LB materials than their low molecular mass analogues. One of the azo dye functionalized polymers forms LB films of exceptional clarity; waveguide losses for 633 nm light were measured at around 2.5 dB cm−1 in a 1.3 μm thick film. Bilayers of the PC functionalized polymer have low-field conductivities of the order of 10−9S m−1, with a transition to a probable space-charge-limited region and eventual breakdown at above 1.5 × 10−8 V m−1. Absorption measurements indicate that bacteriorhodopsin remains active when mixed with the PC functionalized polymer.

This paper describes the previously unreported electrogenerated chemiluminescence (ECL) from the electro-oxidation of several aryl carboxylates at a platinum flag electrode in aqueous, methanolic and acetonitrile solutions using tetramethylammonium hydroxides as a supporting electrolyte. In most cases electrochemiluminescence was markedly enhanced by simultaneous irradiation with ultrasound during electrolysis. Increase in electrochemiluminescence intensity with electrolysis current and carboxylate concentration was observed. Addition of a radical scavenger or purging of the solution with oxygen lowers ECL emission intensity. In contrast the presence of oxygen enhances the intensity of sonoluminescence, which is a concurrent but weaker process occurring under ultrasonic irradiation alone. Ring-substituted phenylacetates almost always produced less electrochemiluminescence than the unsubstituted parent molecule, though within the substituents studied chloro-substituted phenylacetates produced more ECL intensity than either methoxy- or nitro-substituted derivatives.

International audience; Sonochemistry is a technique that offers promise for pollutant degradation, but earlier studies on various chlorinated substrates do not give a definitive view of the effectiveness of this methodology. We now report a thorough study of ultrasonic operational variables upon perchloroethylene (PCE) degradation in water (variables include ultrasonic frequency, power and system geometry as well as substrate concentration) and we attempt to close the mass balance where feasible. We obtained fractional conversions of >97% showing very effective loss of pollutant starting material, and give mechanistic proposals for the reaction pathway based on cavitational phenomena inducing pyrolytic and free radical processes. We note major products of Cl− and CO2/CO, and also trichloroethylene (TCE) and dichloroethylene (DCE) at ppm concentrations as reported earlier. The formation at very low (ppb) concentration of small halocompounds (CHCl3, CCl4) and also of higher-mass species, such as pentachloropropene, hexachloroethane, is noteworthy. But of particular importance in our work is the discovery of significant quantities of chloroacetate derivatives at ppm concentrations. Although these compounds have been described as by-products with other techniques such as radiolysis or photochemistry, this is the first time that these products have been identified in the sonochemical treatment of PCE; this allows a much more effective account of the mass balance and may explain earlier inconsistencies. This reaction system is now better identified, but a corollary is that, because these haloacetates are themselves species of some toxicity, the use of ultrasound here may not sufficiently diminish wastewater toxicity.

The electrochemiluminescence of the tris-(2,2′-bipyridine) ruthenium (II) dication in aqueous oxalate and in acetonitrile containing tetrabutylammonium tetrafluoroborate is markedly enhanced by simultaneous irradiation with 40 and 60 kHz ultrasound: edge effects and electrode patchiness are diminished, reproducibility and stability are improved, electrode fouling is minimised, quantum efficiency is increased and lower cell voltages are required.

We report variously enhanced efficiencies, procedural improvements and altered product distributions from the electrooxidation of phenylacetate and p-chloro phenylacetate anions when performed under simultaneous ultrasonic irradiation.

Tetracyclones are transformed to a mixture of diacylstilbenes and α-pyrones, when they are heated in diphenylether saturated with oxygen.